Microwave oven having integral mixing assembly
FIELD OF THE INVENTION 
     The invention relates to a microwave oven which can cook liquid, semi-liquid and mixable foods such as batters, sauces, stews and the like more evenly than has heretofore been possible. More particularly, the invention relates to a microwave oven having a mixing assembly as an integral part thereof. 
     BACKGROUND OF THE INVENTION 
     Microwave cooking is popular as a quick and convenient way of preparing many types of foods. One important characteristic of microwave cooking is that the food cooks from the outside to the inside. It is therefore known that microwave cooking can cook food unevenly such that the center cooks less than the peripheral areas. This may be an advantageous feature in the preparation of certain food products such as meat where it may be desired to serve the product less well done. In addition, the uneven cooking characteristic of microwave ovens has not been a major drawback in the heating of pre-cooked food products, due to differing food densities. 
     However, the uneven cooking associated with microwave ovens has posed a major problem in the cooking of food products which have not been pre-cooked, such as eggs and sauces. In such instances, the even distribution of heat throughout the food product is crucial to complete and thorough cooking. Uniform cooking is particularly important in the preparation of foods which ordinarily require mixing such as batters, doughs, sauces, stews and the like. Heretofore, microwave cooking has not been particularly suitable for the preparation of such foods which require mixing and a substantially even distribution of heat. At present, the microwave cooking process must be stopped and the oven must be opened so that the food can be stirred. Thus, there is a need for a microwave oven which permits all cooking and stirring operations that might be done on a stove top to be accomplished therein. 
     Accordingly, it is an object of the invention to provide a microwave mixer which ensures that liquid, semi-liquid and mixable foods are uniformly and completely cooked by mixing the same during the cooking process. 
     It is a further object of the invention to provide a microwave oven having an integral mixing means for mixing food in the microwave chamber during cooking. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of the microwave mixer according to the invention. 
     FIG. 2 is a top view of the microwave mixer illustrating drive means for rotating the mixer shaft of the oven. 
     FIG. 3 is an isolated view of the woven metal preform and shie1d retainer plate used in the microwave mixer to abate or prevent leakage of microwaves from the chamber. 
    
    
     SUMMARY OF THE INVENTION 
     The invention provides a microwave oven having an integral mixing assembly for agitating food inside of the cooking cavity during cooking, said mixing assembly including a mixer shaft which is received through a cooking cavity wall and which is capable of rotational movement about its longitudinal axis, the mixer shaft being powered for rotational movement by a motor. The end of the mixer shaft disposed inside of the cooking cavity is adapted for releasable connection to one or more stirring or agitating means. Means may be provided for ensuring that harmful amounts of radiation do not leak from the cooking cavity. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention provides a microwave oven having an integral mixing means for agitating food inside of the microwave chamber. The microwave oven includes a plurality of walls which enclose a microwave chamber or cooking cavity 14. One of the walls is provided with a door (not depicted) for the ingress and egress of food. The microwave oven is conventional in all respects and can be constructed in a well known manner with the exception of the integral mixing means and modifications to accommodate the mixing means which will now be described. 
     Referring to FIG. 1, the top wall 1 of the microwave chamber is provided with a hole for receiving a mixer shaft 2. As illustrated in FIG. 1 the mixer shaft extends into the microwave chamber 14. The mixer shaft 2 must be capable of rotational movement about its longitudinal axis within the chamber wall 1. Any space between the chamber wall 1 and the mixer shaft 2 which is necessary to permit such rotational movement should be minimized such that the oven is opaque to harmful amounts of microwave radiation to prevent leakage. Alternatively, in order to ensure that harmful amounts of microwaves do not emanate from the microwave chamber 14 in the vicinity of the mixer shaft 2, the invention may be provided with a novel means for abating or preventing leakage of the microwaves. The means for preventing leakage is preferably comprised of a shield retainer plate 3 which is attached around the periphery of the mixer shaft 2 on the inside of the microwave chamber such that it rotates with mixer shaft 2 during operation. The shield retainer plate 3 is disposed on the mixer shaft 2 adjacent to the inside of the wall 1 which receives the mixer shaft. The shield retainer plate 3 has a raised lip 4 (see also FIG. 3) for making continuous loose contact with the inner surface of the chamber wall 1 (see FIG. 1) so as to at least attenuate any microwaves attempting to escape through the border and yet allow for the rotational movement of the shield retainer plate 3. Shield retainer plate 3 and its lip 4 as well as the microwave chamber wall 1 are preferably constructed of stainless steel. The face of retainer plate 3 facing the inside of chamber 14 and the inside of the chamber walls may be coated with a layer of a plastic or polysulfone (not depicted). 
     The means for preventing leakage also preferably includes a woven metal preform 5 snugly disposed around the periphery of mixer shaft 2 in the space between the top of the shield retainer plate 3 and the inside surface of the microwave chamber wall 1. The woven metal preform 5 is snugly bordered around its periphery by the lip 4 of shield retainer plate 3. The woven metal preform is preferably comprised of densely packed metal (i.e., stainless steel) fibers and filaments such that it is opaque to microwaves thereby preventing leakage. 
     Thus, it can be seen that in an attempt to escape from the chamber 14 microwaves will first have to traverse the border between the lip 4 of retainer plate 3 and the chamber wall 1. At this border the microwaves will at least be attenuated. If any microwaves manage to cross the border they will be absorbed by woven metal preform 5 which is opaque to harmful amounts of microwaves. Thus, harmful amounts of microwaves cannot escape from the space between the mixer shaft 2 and the microwave chamber wall 1. 
     The invention includes means for rotating mixer shaft 2. This means would include a motor 6 (see FIG. 2) for powering the rotation in either a direct drive fashion or in a belt drive fashion. Direct drive means which are known in the art can be used. A belt drive system is preferred and the invention provides a novel belt drive system and support means which will now be described. 
     Referring to FIG. 2, a drive disc 7 is attached around the periphery of mixer shaft 2 on the outside of the oven. Mixer drive disc 7 receives a belt 8 around an arc of its periphery in a tight pulley like manner (see FIG. 2). Belt 8 couples mixer drive disc 7 for rotational movement with a motor drive disc 9 of motor 6. 
     In this embodiment, mixer drive disc 7 is supported and restricted from all non-rotational movement (i.e., lateral and vertical movement) by a plurality of supports 10, 16 arranged around the periphery of mixer drive disc 7. Supports 10, 16 are constructed like a reel (see FIG. 1) such that the edge of mixer drive disc 7 is sandwiched between the ends of the reel to be restricted from vertical movement. Support reels 10, 16 include a hub 11. Preferably, at least one support reel 16 is positioned directly between mixer drive disc 7 and motor drive disc 9. The periphery of the hub 11 of this support reel 16 abuts the periphery of mixer drive disc 7 to restrict the mixer drive disc 7 (and hence the mixer shaft 2) from lateral movement in the direction of the motor. The periphery of each hub 11 of the other support reels 10 will abut belt 8 around the periphery of mixer drive disc 7 to prevent lateral movement of the mixer drive disc 7 in other directions and to maintain belt 8 around the periphery of mixer drive disc 7. 
     Each support reel 10, 16 is mounted for rotational movement on a mounting axle 12. Mounting axles 12 are attached in an upright manner to the outside surface of top chamber wall 1. There are preferably two supports 10 and one support 16 around mixer drive disc 7 and most preferably, three supports 10 and one support 16. 
     It should be appreciated that supports 10, 16 may be ordinary discs rather than reels if mixer drive disc 7 is constructed as a reel. In this alternative embodiment (not depicted): the support discs will be sandwiched by the mixer drive reel to restrict vertical movement of the mixer drive reel, belt 8 will be wrapped around an arc of the hub of the mixer drive reel; and the periphery of the support discs will abut the hub of the mixer drive reel (or the belt around the hub as the case may be) to restrict lateral movement of the mixer drive reel. 
     Mixer drive disc 7 (and hence mixer shaft 2) may also be supported on one end of a spring 13 which is disposed around mixer shaft 2 (see FIG. 1). The other end of spring 13 rests on the top of chamber wall 1 for supporting the mixer drive disc 7 (and hence the mixer shaft 2). 
     Various stirrers or other beaters 15 may be attached to the mixer shaft 2 depending upon the type of mixing or blending which is desired during cooking. The stirrer 15 and the portion of the mixer shaft 2 disposed inside the cooking cavity 14 are coated with a plastic or a well known polysulfone coating. 
     It can be seen from the foregoing description that the invention provides a microwave mixer which allows for the mixing of food in the microwave chamber during cooking. In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than a restrictive sense.